1. Field of the Invention
The present invention relates to a semiconductor device and, more particularly, to a semiconductor device having characteristics suitable for forming a drive circuit for a power integrated circuit (hereinafter referred to as xe2x80x9cpower ICxe2x80x9d).
2. Background Art
Some driver circuit of a power IC includes a bipolar transistor. FIG. 1 is a sectional view of a semiconductor device including a bipolar transistor, for the driver circuit of a power IC and FIG. 2 is a sectional view of assistance in explaining the operation of the semiconductor device shown in FIG. 1.
Referring to FIG. 1, the semiconductor device has a p-type semiconductor substrate 10. An n-type collector region 12 is formed in an upper part of the semiconductor substrate 10. A p-type base region 14 is formed in the surface of the collector region 12. An n-type emitter region 16 is formed in the surface of the base region 14.
The collector region 12, the base region 14 and the emitter region 16 constitute a bipolar transistor. A buried region 18 of a width slightly greater than that of the emitter region 16 is formed in the vicinity of the boundary between the semiconductor substrate 10 and the collector region 12. The buried region 18 is a region of an n+-type semiconductor formed by diffusion. The buried layer 18 reduces the collector resistance of the bipolar transistor and suppresses the flow of leakage current from the bipolar transistor to the semiconductor substrate 10.
The driver circuit of the power IC needs a transistor for supplying power to a circuit to be driven (hereinafter referred to as xe2x80x9cdriven circuitxe2x80x9d), and a diode for discharging electric energy accumulated in an inductor component (hereinafter referred to as xe2x80x9cinductorxe2x80x9d) of the driven circuit. In the semiconductor device shown in FIG. 1, the joint of the semiconductor substrate 10 and the collector region 12 forms a diode 20 (hereinafter referred to as xe2x80x9ccollector/substrate diode 20xe2x80x9d). The semiconductor device shown in FIG. 1 is suitable for forming the driver circuit of the power IC in a compact structure.
In FIG. 2, the semiconductor substrate 10 of the semiconductor device is grounded, and the collector region 12 is connected to an inductor 22. The collector/substrate diode 20 permits a current to flow from the semiconductor substrate 10 into the inductor 22, so that electric energy accumulated in the inductor 22 can be discharged.
Time necessary to discharge the electric energy accumulated in the inductor 22 is dependent on the operating speed of the collector/substrate diode 20. It is desirable that the electrical energy can be discharged in a short time in view of suppressing of a power loss in the driver circuit; that is, it is desirable that the operating speed of the collector/substrate diode 20 is high. However, a structural restriction makes it difficult for the collector/substrate diode 20 to operate at a high operating speed. Consequently, the driver circuit employing the conventional semiconductor device is apt to involve a large power loss.
The present invention has been made to solve the foregoing problems and it is therefore an object of the present invention to provide a semiconductor device of construction suitable for forming a driver circuit.
According to one aspect of the present invention, a semiconductor device comprises a semiconductor substrate, a bipolar transistor formed on the semiconductor substrate and having a collector region, a Schottky diode formed in the collector region of the bipolar transistor, and a potential isolating layer isolating the collector region and the semiconductor substrate in potential from each other.
Other and further objects, features and advantages of the invention will appear more fully from the following description.